Mixed mode preamble for MIMO wireless communications

ABSTRACT

A preamble of a frame for a multiple input multiple output (MIMO) wireless communication for a first transmit antenna of the MIMO communication includes a legacy preamble portion in accordance with a legacy wireless communication protocol. The preamble of the frame for the MIMO wireless communication for the first transmit antenna also includes a current protocol preamble portion in accordance with a protocol of the MIMO wireless communication. The preamble of a frame for at least a second antenna of the MIMO communication includes a cyclically shifted legacy preamble portion for the frame. The preamble of the frame for the MIMO wireless communication for the second transmit antenna also includes a second current protocol preamble portion in accordance with a protocol of the MIMO wireless communication.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present U.S. Utility patent application claims priority pursuant to35 U.S.C. §120, as a continuation, to U.S. Utility application Ser. No.11/079,962, entitled “MIXED MODE PREAMBLE FOR MIMO WIRELESSCOMMUNICATIONS,” filed Mar. 15, 2005, pending, which claims priority tothe following applications:

-   -   Pursuant to 35 U.S.C. §120, as a continuation-in-part, to U.S.        Utility application Ser. No. 10/973,595 entitled “PREAMBLE        FORMATS FOR MIMO WIRELESS COMMUNICATIONS,” filed Oct. 26, 2004,        now U.S. Pat. No. 7,423,989; and    -   Pursuant to 35 U.S.C. §119(e) to U.S. Provisional Application        Ser. No. 60/651,100, entitled “MIXED MODE PREAMBLE FOR MIMO        WIRELESS COMMUNICATIONS,” filed Feb. 8, 2005, expired;        all of which are incorporated herein by reference in their        entirety and made part of the present U.S. Utility patent        application for all purposes.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

This invention relates generally to wireless communication systems andmore particularly to supporting multiple wireless communicationprotocols within a wireless local area network.

The present U.S. Utility patent application claims priority pursuant to35 U.S.C. §120, as a continuation in part, to U.S. Utility applicationSer. No. 12/173,796, entitled “PREAMBLE FORMATS FOR MIMO WIRELESSCOMMUNICATIONS,” filed Jul. 15, 2008, pending, which claims prioritypursuant to 35 U.S.C. §120, as a continuation, to U.S. Utilityapplication Ser. No. 10/973,595 entitled “PREAMBLE FORMATS FOR MIMOWIRELESS COMMUNICATIONS,” filed Oct. 26, 2004, now U.S. Pat. No.7,423,989, all of which are incorporated herein by reference in theirentirety and made part of the present U.S. Utility patent applicationfor all purposes.

2. Description of Related Art

Communication systems are known to support wireless and wire linedcommunications between wireless and/or wire lined communication devices.Such communication systems range from national and/or internationalcellular telephone systems to the Internet to point-to-point in-homewireless networks. Each type of communication system is constructed, andhence operates, in accordance with one or more communication standards.For instance, wireless communication systems may operate in accordancewith one or more standards including, but not limited to, IEEE 802.11,Bluetooth, advanced mobile phone services (AMPS), digital AMPS, globalsystem for mobile communications (GSM), code division multiple access(CDMA), local multi-point distribution systems (LMDS),multi-channel-multi-point distribution systems (MMDS), and/or variationsthereof.

Depending on the type of wireless communication system, a wirelesscommunication device, such as a cellular telephone, two-way radio,personal digital assistant (PDA), personal computer (PC), laptopcomputer, home entertainment equipment, et cetera communicates directlyor indirectly with other wireless communication devices. For directcommunications (also known as point-to-point communications), theparticipating wireless communication devices tune their receivers andtransmitters to the same channel or channels (e.g., one of the pluralityof radio frequency (RF) carriers of the wireless communication system)and communicate over that channel(s). For indirect wirelesscommunications, each wireless communication device communicates directlywith an associated base station (e.g., for cellular services) and/or anassociated access point (e.g., for an in-home or in-building wirelessnetwork) via an assigned channel. To complete a communication connectionbetween the wireless communication devices, the associated base stationsand/or associated access points communicate with each other directly,via a system controller, via the public switch telephone network, viathe Internet, and/or via some other wide area network.

For each wireless communication device to participate in wirelesscommunications, it includes a built-in radio transceiver (i.e., receiverand transmitter) or is coupled to an associated radio transceiver (e.g.,a station for in-home and/or in-building wireless communicationnetworks, RF modem, etc.). As is known, the transmitter includes a datamodulation stage, one or more intermediate frequency stages, and a poweramplifier. The data modulation stage converts raw data into basebandsignals in accordance with a particular wireless communication standard.The one or more intermediate frequency stages mix the baseband signalswith one or more local oscillations to produce RF signals. The poweramplifier amplifies the RF signals prior to transmission via an antenna.

As is also known, the receiver is coupled to the antenna and includes alow noise amplifier, one or more intermediate frequency stages, afiltering stage, and a data recovery stage. The low noise amplifierreceives inbound RF signals via the antenna and amplifies then. The oneor more intermediate frequency stages mix the amplified RF signals withone or more local oscillations to convert the amplified RF signal intobaseband signals or intermediate frequency (IF) signals. The filteringstage filters the baseband signals or the IF signals to attenuateunwanted out of band signals to produce filtered signals. The datarecovery stage recovers raw data from the filtered signals in accordancewith the particular wireless communication standard.

As is further known, the standard to which a wireless communicationdevice is compliant within a wireless communication system may vary. Forinstance, as the IEEE 802.11 specification has evolved from IEEE 802.11to IEEE 802.11b to IEEE 802.11a and to IEEE 802.11g, wirelesscommunication devices that are compliant with IEEE 802.11b may exist inthe same wireless local area network (WLAN) as IEEE 802.11g compliantwireless communication devices. As another example, IEEE 802.11acompliant wireless communication devices may reside in the same WLAN asIEEE 802.11g compliant wireless communication devices. When legacydevices (i.e., those compliant with an earlier version of a standard)reside in the same WLAN as devices compliant with later versions of thestandard, a mechanism is employed to insure that legacy devices knowwhen the newer version devices are utilizing the wireless channel as toavoid a collision.

For instance, backward compatibility with legacy devices has beenenabled exclusively at either the physical (PHY) layer (in the case ofIEEE 802.11b) or the Media-Specific Access Control (MAC) layer (in thecase of 802.11g). At the PHY layer, backward compatibility is achievedby re-using the PHY preamble from a previous standard. In this instance,legacy devices will decode the preamble portion of all signals, whichprovides sufficient information for determining that the wirelesschannel is in use for a specific period of time, thereby avoidcollisions even though the legacy devices cannot fully demodulate and/ordecode the transmitted frame(s).

At the MAC layer, backward compatibility with legacy devices is enabledby forcing devices that are compliant with a newer version of thestandard to transmit special frames using modes or data rates that areemployed by legacy devices. For example, the newer devices may transmitClear to Send/Ready to Send (CTS/RTS) exchange frames and/or CTS to selfframes as are employed in IEEE 802.11g. These special frames containinformation that sets the NAV (network allocation vector) of legacydevices such that these devices know when the wireless channel is in useby newer stations.

Both of the existing mechanisms for backward compatibility suffer from aperformance loss relative to that which can be achieved without backwardcompatibility and are used independently of each other.

Therefore, a need exists for a method and apparatus that enablesmultiple protocols to be supported within a wireless communicationsystem, including wireless local area networks.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to apparatus and methods of operationthat are further described in the following Brief Description of theDrawings, the Detailed Description of the Invention, and the claims.Other features and advantages of the present invention will becomeapparent from the following detailed description of the invention madewith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a wireless communication systemin accordance with the present invention;

FIG. 2 is a schematic block diagram of a wireless communication devicein accordance with the present invention;

FIG. 3 is a schematic block diagram of another wireless communicationdevice in accordance with the present invention;

FIG. 4 is a schematic block diagram of an RF transmitter in accordancewith the present invention;

FIG. 5 is a schematic block diagram of an RF receiver in accordance withthe present invention;

FIG. 6 is a schematic block diagram of an access point communicatingwith wireless communication devices in accordance with the presentinvention;

FIG. 7 is a diagram depicting a MIMO wireless communication inaccordance with the present invention; and

FIG. 8 is a diagram of an example preamble of the MIMO communication ofFIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram illustrating a communication system10 that includes a plurality of base stations and/or access points12-16, a plurality of wireless communication devices 18-32 and a networkhardware component 34. The wireless communication devices 18-32 may belaptop host computers 18 and 26, personal digital assistant hosts 20 and30, personal computer hosts 24 and 32 and/or cellular telephone hosts 22and 28. The details of the wireless communication devices will bedescribed in greater detail with reference to FIGS. 2 and/or 3.

The base stations or access points 12-16 are operably coupled to thenetwork hardware 34 via local area network connections 36, 38 and 40.The network hardware 34, which may be a router, switch, bridge, modem,system controller, et cetera provides a wide area network connection 42for the communication system 10. Each of the base stations or accesspoints 12-16 has an associated antenna or antenna array to communicatewith the wireless communication devices in its regional area, which isgenerally referred to as a basic service set (BSS) 9, 11, 13. Typically,the wireless communication devices register with a particular basestation or access point 12-14 to receive services from the communicationsystem 10. For direct connections (i.e., point-to-point communications),wireless communication devices communicate directly via an allocatedchannel to produce an ad-hoc network.

Typically, base stations are used for cellular telephone systems andlike-type systems, while access points are used for in-home orin-building wireless networks. Regardless of the particular type ofcommunication system, each wireless communication device includes abuilt-in radio and/or is coupled to a radio. The radio includes a highlylinear amplifier and/or programmable multi-stage amplifier as disclosedherein to enhance performance, reduce costs, reduce size, and/or enhancebroadband applications.

FIG. 2 is a schematic block diagram illustrating a wirelesscommunication device that includes the host device 18-32 and anassociated radio 60. For cellular telephone hosts, the radio 60 is abuilt-in component. For personal digital assistants hosts, laptop hosts,and/or personal computer hosts, the radio 60 may be built-in or anexternally coupled component.

As illustrated, the host device 18-32 includes a processing module 50,memory 52, radio interface 54, input interface 58 and output interface56. The processing module 50 and memory 52 execute the correspondinginstructions that are typically done by the host device. For example,for a cellular telephone host device, the processing module 50 performsthe corresponding communication functions in accordance with aparticular cellular telephone standard.

The radio interface 54 allows data to be received from and sent to theradio 60. For data received from the radio 60 (e.g., inbound data), theradio interface 54 provides the data to the processing module 50 forfurther processing and/or routing to the output interface 56. The outputinterface 56 provides connectivity to an output display device such as adisplay, monitor, speakers, et cetera such that the received data may bedisplayed. The radio interface 54 also provides data from the processingmodule 50 to the radio 60. The processing module 50 may receive theoutbound data from an input device such as a keyboard, keypad,microphone, et cetera via the input interface 58 or generate the dataitself. For data received via the input interface 58, the processingmodule 50 may perform a corresponding host function on the data and/orroute it to the radio 60 via the radio interface 54.

Radio 60 includes a host interface 62, digital receiver processingmodule 64, memory 75, a digital transmitter processing module 76, and aradio transceiver. The radio transceiver includes an analog-to-digitalconverter 66, a filtering/gain module 68, an IF mixing down conversionstage 70, a receiver filter 71, a low noise amplifier 72, atransmitter/receiver switch 73, a local oscillation module 74, adigital-to-analog converter 78, a filtering/gain module 80, an IF mixingup conversion stage 82, a power amplifier 84, a transmitter filtermodule 85, and an antenna 86. The antenna 86 may be a single antennathat is shared by the transmit and receive paths as regulated by theTx/Rx switch 73, or may include separate antennas for the transmit pathand receive path. The antenna implementation will depend on theparticular standard to which the wireless communication device iscompliant.

The digital receiver processing module 64 and the digital transmitterprocessing module 76, in combination with operational instructionsstored in memory 75, execute digital receiver functions and digitaltransmitter functions, respectively, in accordance with one or morewireless communication standards and as further function to implementone or more aspects of the functionality described with reference toFIGS. 3-11. The digital receiver functions include, but are not limitedto, digital intermediate frequency to baseband conversion, demodulation,constellation demapping, decoding, and/or descrambling. The digitaltransmitter functions include, but are not limited to, scrambling,encoding, constellation mapping, modulation, and/or digital baseband toIF conversion. The digital receiver and transmitter processing modules64 and 76 may be implemented using a shared processing device,individual processing devices, or a plurality of processing devices.Such a processing device may be a microprocessor, micro-controller,digital signal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, analog circuitry, digital circuitry, and/or any device thatmanipulates signals (analog and/or digital) based on operationalinstructions. The memory 75 may be a single memory device or a pluralityof memory devices. Such a memory device may be a read-only memory,random access memory, volatile memory, non-volatile memory, staticmemory, dynamic memory, flash memory, and/or any device that storesdigital information. Note that when the processing module 64 and/or 76implements one or more of its functions via a state machine, analogcircuitry, digital circuitry, and/or logic circuitry, the memory storingthe corresponding operational instructions is embedded with thecircuitry comprising the state machine, analog circuitry, digitalcircuitry, and/or logic circuitry.

In operation, the radio 60 receives outbound data 94 from the hostdevice via the host interface 62. The host interface 62 routes theoutbound data 94 to the digital transmitter processing module 76, whichprocesses the outbound data 94 in accordance with a particular wirelesscommunication standard (e.g., IEEE 802.11 and versions thereof,Bluetooth and versions thereof, et cetera) to produce digitaltransmission formatted data 96. The digital transmission formatted data96 will be a digital base-band signal or a digital low IF signal, wherethe low IF typically will be in the frequency range of one hundredkilohertz to a few megahertz.

The digital-to-analog converter 78 converts the digital transmissionformatted data 96 from the digital domain to the analog domain. Thefiltering/gain module 80 filters and/or adjusts the gain of the analogsignal prior to providing it to the IF mixing stage 82. The IF mixingstage 82 converts the analog baseband or low IF signal into an RF signalbased on a transmitter local oscillation 83 provided by localoscillation module 74. The power amplifier 84 amplifies the RF signal toproduce outbound RF signal 98, which is filtered by the transmitterfilter module 85. The antenna 86 transmits the outbound RF signal 98 toa targeted device such as a base station, an access point and/or anotherwireless communication device.

The radio 60 also receives an inbound RF signal 88 via the antenna 86,which was transmitted by a base station, an access point, or anotherwireless communication device. The antenna 86 provides the inbound RFsignal 88 to the receiver filter module 71 via the Tx/Rx switch 73,where the Rx filter 71 bandpass filters the inbound RF signal 88. The Rxfilter 71 provides the filtered RF signal to low noise amplifier 72,which amplifies the signal 88 to produce an amplified inbound RF signal.The low noise amplifier 72 provides the amplified inbound RF signal tothe IF mixing module 70, which directly converts the amplified inboundRF signal into an inbound low IF signal or baseband signal based on areceiver local oscillation 81 provided by local oscillation module 74.The down conversion module 70 provides the inbound low IF signal orbaseband signal to the filtering/gain module 68. The filtering/gainmodule 68 filters and/or gains the inbound low IF signal or the inboundbaseband signal to produce a filtered inbound signal.

The analog-to-digital converter 66 converts the filtered inbound signalfrom the analog domain to the digital domain to produce digitalreception formatted data 90. The digital receiver processing module 64decodes, descrambles, demaps, and/or demodulates the digital receptionformatted data 90 to recapture inbound data 92 in accordance with theparticular wireless communication standard being implemented by radio60. The host interface 62 provides the recaptured inbound data 92 to thehost device 18-32 via the radio interface 54.

As one of average skill in the art will appreciate, the wirelesscommunication device of FIG. 2 may be implemented using one or moreintegrated circuits. For example, the host device may be implemented onone integrated circuit, the digital receiver processing module 64, thedigital transmitter processing module 76 and memory 75 may beimplemented on a second integrated circuit, and the remaining componentsof the radio 60, less the antenna 86, may be implemented on a thirdintegrated circuit. As an alternate example, the radio 60 may beimplemented on a single integrated circuit. As yet another example, theprocessing module 50 of the host device and the digital receiver andtransmitter processing modules 64 and 76 may be a common processingdevice implemented on a single integrated circuit. Further, the memory52 and memory 75 may be implemented on a single integrated circuitand/or on the same integrated circuit as the common processing modulesof processing module 50 and the digital receiver and transmitterprocessing module 64 and 76.

FIG. 3 is a schematic block diagram illustrating a wirelesscommunication device that includes the host device 18-32 and anassociated radio 60. For cellular telephone hosts, the radio 60 is abuilt-in component. For personal digital assistants hosts, laptop hosts,and/or personal computer hosts, the radio 60 may be built-in or anexternally coupled component.

Radio 60 includes a host interface 62, a baseband processing module 63,memory 65, a plurality of radio frequency (RF) transmitters 67, 69, 71,a transmit/receive (T/R) module 73, a plurality of antennas 81, 83, 85,a plurality of RF receivers 75, 77, 79, and a local oscillation module99. The baseband processing module 63, in combination with operationalinstructions stored in memory 65, execute digital receiver functions anddigital transmitter functions, respectively. The digital receiverfunctions include, but are not limited to, digital intermediatefrequency to baseband conversion, demodulation, constellation demapping,decoding, de-interleaving, fast Fourier transform, cyclic prefixremoval, space and time decoding, and/or descrambling. The digitaltransmitter functions include, but are not limited to, scrambling,encoding, interleaving, constellation mapping, modulation, inverse fastFourier transform, cyclic prefix addition, space and time encoding,and/or digital baseband to IF conversion. The baseband processingmodules 63 may be implemented using one or more processing devices. Sucha processing device may be a microprocessor, micro-controller, digitalsignal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, analog circuitry, digital circuitry, and/or any device thatmanipulates signals (analog and/or digital) based on operationalinstructions. The memory 66 may be a single memory device or a pluralityof memory devices. Such a memory device may be a read-only memory,random access memory, volatile memory, non-volatile memory, staticmemory, dynamic memory, flash memory, and/or any device that storesdigital information. Note that when the processing module 63 implementsone or more of its functions via a state machine, analog circuitry,digital circuitry, and/or logic circuitry, the memory storing thecorresponding operational instructions is embedded with the circuitrycomprising the state machine, analog circuitry, digital circuitry,and/or logic circuitry.

In operation, the radio 60 receives outbound data 87 from the hostdevice via the host interface 62. The baseband processing module 63receives the outbound data 87 and, based on a mode selection signal 101,produces one or more outbound symbol streams 89. The mode selectionsignal 101 will indicate a particular mode as are indicated in modeselection tables. For example, the mode selection signal 101, withreference to table 1 may indicate a frequency band of 2.4 GHz, a channelbandwidth of 20 or 22 MHz and a maximum bit rate of 54megabits-per-second. In this general category, the mode selection signalwill further indicate a particular rate ranging from 1megabit-per-second to 54 megabits-per-second. In addition, the modeselection signal will indicate a particular type of modulation, whichincludes, but is not limited to, Barker Code Modulation, BPSK, QPSK,CCK, 16 QAM and/or 64 QAM. As is further illustrated in table 1, a coderate is supplied as well as number of coded bits per subcarrier (NBPSC),coded bits per OFDM symbol (NCBPS), data bits per OFDM symbol (NDBPS),error vector magnitude in decibels (EVM), sensitivity which indicatesthe maximum receive power required to obtain a target packet error rate(e.g., 10% for IEEE 802.11a), adjacent channel rejection (ACR), and analternate adjacent channel rejection (AACR).

The mode selection signal may also indicate a particular channelizationfor the corresponding mode which for the information in table 1 isillustrated in table 2. As shown, table 2 includes a channel number andcorresponding center frequency. The mode select signal may furtherindicate a power spectral density mask value which for table 1 isillustrated in table 3. The mode select signal may alternativelyindicate rates within table 4 that has a 5 GHz frequency band, 20 MHzchannel bandwidth and a maximum bit rate of 54 megabits-per-second. Ifthis is the particular mode select, the channelization is illustrated intable 5. As a further alternative, the mode select signal 102 mayindicate a 2.4 GHz frequency band, 20 MHz channels and a maximum bitrate of 192 megabits-per-second as illustrated in table 6. In table 6, anumber of antennas may be utilized to achieve the higher bandwidths. Inthis instance, the mode select would further indicate the number ofantennas to be utilized. Table 7 illustrates the channelization for theset-up of table 6. Table 8 illustrates yet another mode option where thefrequency band is 2.4 GHz, the channel bandwidth is 20 MHz and themaximum bit rate is 192 megabits-per-second. The corresponding table 8includes various bit rates ranging from 12 megabits-per-second to 216megabits-per-second utilizing 2-4 antennas and a spatial time encodingrate as indicated. Table 9 illustrates the channelization for table 8.The mode select signal 102 may further indicate a particular operatingmode as illustrated in table 10, which corresponds to a 5 GHz frequencyband having 40 MHz frequency band having 40 MHz channels and a maximumbit rate of 486 megabits-per-second. As shown in table 10, the bit ratemay range from 13.5 megabits-per-second to 486 megabits-per-secondutilizing 1-4 antennas and a corresponding spatial time code rate. Table10 further illustrates a particular modulation scheme code rate andNBPSC values. Table 11 provides the power spectral density mask fortable 10 and table 12 provides the channelization for table 10.

The baseband processing module 63, based on the mode selection signal101 produces the one or more outbound symbol streams 89 from the outputdata 88. For example, if the mode selection signal 101 indicates that asingle transmit antenna is being utilized for the particular mode thathas been selected, the baseband processing module 63 will produce asingle outbound symbol stream 89. Alternatively, if the mode selectsignal indicates 2, 3 or 4 antennas, the baseband processing module 63will produce 2, 3 or 4 outbound symbol streams 89 corresponding to thenumber of antennas from the output data 88.

Depending on the number of outbound streams 89 produced by the basebandmodule 63, a corresponding number of the RF transmitters 67, 69, 71 willbe enabled to convert the outbound symbol streams 89 into outbound RFsignals 91. The implementation of the RF transmitters 67, 69, 71 will befurther described with reference to FIG. 4. The transmit/receive module73 receives the outbound RF signals 91 and provides each outbound RFsignal to a corresponding antenna 81, 83, 85.

When the radio 60 is in the receive mode, the transmit/receive module 73receives one or more inbound RF signals via the antennas 81, 83, 85. TheT/R module 73 provides the inbound RF signals 93 to one or more RFreceivers 75, 77, 79. The RF receiver 75, 77, 79, which will bedescribed in greater detail with reference to FIG. 4, converts theinbound RF signals 93 into a corresponding number of inbound symbolstreams 96. The number of inbound symbol streams 95 will correspond tothe particular mode in which the data was received (recall that the modemay be any one of the modes illustrated in tables 1-12). The basebandprocessing module 63 receives the inbound symbol streams 89 and convertsthem into inbound data 97, which is provided to the host device 18-32via the host interface 62.

As one of average skill in the art will appreciate, the wirelesscommunication device of FIG. 3 may be implemented using one or moreintegrated circuits. For example, the host device may be implemented onone integrated circuit, the baseband processing module 63 and memory 65may be implemented on a second integrated circuit, and the remainingcomponents of the radio 60, less the antennas 81, 83, 85, may beimplemented on a third integrated circuit. As an alternate example, theradio 60 may be implemented on a single integrated circuit. As yetanother example, the processing module 50 of the host device and thebaseband processing module 63 may be a common processing deviceimplemented on a single integrated circuit. Further, the memory 52 andmemory 65 may be implemented on a single integrated circuit and/or onthe same integrated circuit as the common processing modules ofprocessing module 50 and the baseband processing module 63.

FIG. 4 is a schematic block diagram of an embodiment of an RFtransmitter 67, 69, 71. The RF transmitter includes a digital filter andup-sampling module 475, a digital-to-analog conversion module 477, ananalog filter 479, and up-conversion module 81, a power amplifier 483and a RF filter 485. The digital filter and up-sampling module 475receives one of the outbound symbol streams 89 and digitally filters itand then up-samples the rate of the symbol streams to a desired rate toproduce the filtered symbol streams 487. The digital-to-analogconversion module 477 converts the filtered symbols 487 into analogsignals 489. The analog signals may include an in-phase component and aquadrature component.

The analog filter 479 filters the analog signals 489 to produce filteredanalog signals 491. The up-conversion module 481, which may include apair of mixers and a filter, mixes the filtered analog signals 491 witha local oscillation 493, which is produced by local oscillation module99, to produce high frequency signals 495. The frequency of the highfrequency signals 495 corresponds to the frequency of the RF signals492.

The power amplifier 483 amplifies the high frequency signals 495 toproduce amplified high frequency signals 497. The RF filter 485, whichmay be a high frequency band-pass filter, filters the amplified highfrequency signals 497 to produce the desired output RF signals 91.

As one of average skill in the art will appreciate, each of the radiofrequency transmitters 67, 69, 71 will include a similar architecture asillustrated in FIG. 4 and further include a shut-down mechanism suchthat when the particular radio frequency transmitter is not required, itis disabled in such a manner that it does not produce interferingsignals and/or noise.

FIG. 5 is a schematic block diagram of each of the RF receivers 75, 77,79. In this embodiment, each of the RF receivers includes an RF filter501, a low noise amplifier (LNA) 503, a programmable gain amplifier(PGA) 505, a down-conversion module 507, an analog filter 509, ananalog-to-digital conversion module 511 and a digital filter anddown-sampling module 513. The RF filter 501, which may be a highfrequency band-pass filter, receives the inbound RF signals 93 andfilters them to produce filtered inbound RF signals. The low noiseamplifier 503 amplifies the filtered inbound RF signals 93 based on again setting and provides the amplified signals to the programmable gainamplifier 505. The programmable gain amplifier further amplifies theinbound RF signals 93 before providing them to the down-conversionmodule 507.

The down-conversion module 507 includes a pair of mixers, a summationmodule, and a filter to mix the inbound RF signals with a localoscillation (LO) that is provided by the local oscillation module toproduce analog baseband signals. The analog filter 509 filters theanalog baseband signals and provides them to the analog-to-digitalconversion module 511 which converts them into a digital signal. Thedigital filter and down-sampling module 513 filters the digital signalsand then adjusts the sampling rate to produce the inbound symbol stream95.

FIG. 6 is a schematic block diagram of an access point 12-16communicating with wireless communication devices 25, 27 and/or 29. Thewireless communication devices 25, 27 and/or 29 may be any one of thedevices 18-32 illustrated in FIGS. 1-3. In this illustration, accesspoint 12-16 includes a processing module 15, memory 17 and a radiotransceiver 19. The radio transceiver 19 may be similar to the radiotransceiver of each wireless communication device in architecture andmay include a plurality of antennas, transmit paths and receive pathsfor multiple wireless communications within a proximal region or basicservice set. The processing module 15 may be a single processing deviceor a plurality of processing devices. Such a processing device may be amicroprocessor, micro-controller, digital signal processor,microcomputer, central processing unit, field programmable gate array,programmable logic device, state machine, logic circuitry, analogcircuitry, digital circuitry, and/or any device that manipulates signals(analog and/or digital) based on operational instructions. The memory 17may be a single memory device or a plurality of memory devices. Such amemory device may be a read-only memory, random access memory, volatilememory, non-volatile memory, static memory, dynamic memory, flashmemory, cache memory, and/or any device that stores digital information.Note that when the processing module 15 implements one or more of itsfunctions via a state machine, analog circuitry, digital circuitry,and/or logic circuitry, the memory storing the corresponding operationalinstructions may be embedded within, or external to, the circuitrycomprising the state machine, analog circuitry, digital circuitry,and/or logic circuitry. The memory 17 stores, and the processing module15 executes, operational instructions corresponding to at least some ofthe steps and/or functions illustrated in FIGS. 7-32.

In this illustration, each of the wireless communication devices 25, 27and 29 utilize a different wireless communication protocol. Asillustrated, wireless communication device 25 utilizes protocol A 35,wireless communication device 27 utilizes protocol B 37 and wirelesscommunication device 29 utilizes protocol C 39. For example, protocolsA, B and C may correspond to different versions of the IEEE 802.11standard. In particular, protocol A may correspond to IEEE 802.11b,protocol B may correspond to IEEE 802.11g and protocol C may correspondto IEEE 802.11n.

The protocols may be ordered in accordance with a protocol orderingtable that has protocol A, protocol B and protocol C listed in order.The ordering may be based on the legacy of each of the correspondingprotocols where the first protocol in the ordering is the oldeststandard and the last entry in the protocol ordering is the most currentstandard. For example, in this present illustration protocol A maycorrespond to IEEE 802.11b, protocol B may correspond to IEEE 802.11gand protocol C may correspond to IEEE 802.11n. Alternatively, theprotocol ordering may be based on a user defined and/or systemadministrator defined procedure. For instance, if an unacceptable numberof transmission errors occur due to non-recognition of frames whileutilizing protocol A to set-up wireless communications, the user mayselect the protocol B format for setting up a wireless communication.This concept will be described in greater detail with reference to theremaining figures.

In operation, the access point 12-16, and/or each of the wirelesscommunication devices 25, 27 and 29, determine the protocol utilized byeach of the wireless communication devices within the proximal region.Recall that the proximal region may include a basic service set and/orneighboring basic service sets and/or a direct, or ad-hoc networkwherein the wireless communication devices communicate directly. Oncethe protocol of each of the wireless communication devices has beendetermined, the access point 12-16 and/or the wireless communicationdevices 25-29 determine, based on the protocol ordering, which protocolwill be utilized to set-up a wireless communication. For instance, ifprotocol A corresponds to IEEE 802.11b, the communication devices willutilize a MAC level protection mechanism to set-up a wirelesscommunication. As such, each of the wireless communication devices willutilize protocol A to set-up, or establish, a wireless communicationsuch that the legacy devices recognize that a wireless communication isbeing set-up and also recognizes the duration of that wirelesscommunication such that it will not transmit during that time, thusavoiding a collision.

Once the wireless communication is established, or set-up, utilizing aselected protocol (e.g., protocol A) from the protocol ordering, thecommunication device then utilizes its protocol to transmit the data forthe remainder of the wireless communication. For example, wirelesscommunication device 25 will utilize protocol A to establish and totransmit data for a wireless communication. Wireless communicationdevice 27 will utilize protocol A to set-up a wireless communication andthen use protocol B for the corresponding data transmission of thewireless communication. Similarly, wireless communication device 29 willutilize protocol A to establish, or set-up, the wireless communicationand then use protocol C for the data transmission portion of thewireless communication.

As one of average skill in the art will appreciate, if the proximalregion only includes wireless communication devices that utilize thesame protocol, the set-up and data transmission is done using thatprotocol. As one of average skill in the art will further appreciate, ifonly two different protocols are present within the proximal region, thelegacy protocol will be selected as the set-up protocol.

FIG. 7 is a diagram of a wireless communication between two wirelesscommunication devices 100 and 102, each of which is compliant with IEEE802.11n. Such a communication is taking place within a proximal areathat includes 802.11n compliant devices, 802.11a compliant devicesand/or 802.11g compliant devices. In this instance, the wirelesscommunication may be direct or indirect where a frame 110 includes afirst transmit antenna portion 110-1 and a second transmit antennaportion 110-2. The first transmit antenna portion 110-1 includes apreamble and a data section 108. The preamble includes a legacy portion112 and a current protocol portion 114, remaining set-up informationportion 114. The second transmit antenna portion 110-2 includes a secondpreamble and a second data section 108-1. The second preamble includes acyclically shifted legacy portion 112-1 and a second current protocolportion 114-1.

The legacy portion 112 of the preamble is formatted in accordance withone or more legacy wireless communication standards including, but notlimited to, GSM, IEEE 802.11(a), (b), (g), (j), Bluetooth, or versionsthereof. Further, the legacy portion 112 includes at least a firsttraining sequence and a second training sequence. Such trainingsequences are used to detect a signal, signal characteristics, and frameduration. The cyclically shifted legacy portion 112-1 of the preambleincludes a cyclically shifted first training sequence and a cyclicallyshifted second training sequence. Note that the cyclically shiftedlegacy portion 112-1 of the preamble may include more cyclically shiftedtraining sequences if the legacy portion 112 of the preamble includesmore than two training sequences.

The cyclically shifted first training sequence is a replica of the firsttraining sequence shifted in time with respect to the first trainingsequence. The shift in time is a fraction of the duration the preambleof the frame 110. For instance, the fraction of the duration of thepreamble may range from +50 nanoseconds to +400 nanoseconds or rangefrom −50 nanoseconds to −400 nanoseconds. The cyclically shifted secondtraining sequence is a replica of the second training sequence shiftedin time with respect to the first training sequence by the fraction ofthe duration of the preamble.

The current protocol preamble portion 114 and the second currentprotocol preamble portion 114-1 include additional training sequencesfor wireless communication devices that are compliant with the currentwireless communication protocol (e.g., IEEE 802.11n). For instance, thecurrent protocol preamble portion 114 may include additionalsupplemental long training sequences, which are each 4 microseconds induration, a high data signal field, which is 4 microseconds in duration,to provide additional information regarding the frame. The data portion108 includes the data symbols, which are 4 microseconds in duration. Inthis instance, the legacy protection is provided at the physical layer.

FIG. 8 is a diagram of an example preamble of the MIMO communication ofFIG. 7. In this example, the current wireless protocol is IEEE 802.11nand the legacy wireless communication protocol is IEEE 802.11(a) and/or(g). As is shown, the first transmit antenna frame portion 110-1includes symbols of a short training sequence (STS) 120 as the firsttraining sequence of the legacy portion 112 of the preamble, a doubleguard interval (GI2) 122, symbols of a long training sequence (LTS) 124,126—repeated twice—as the second training sequence of the legacy portion112 of the preamble, a guard interval (GI) 128, and a signal field 129.The second transmit antenna frame portion 110-2 includes cyclicallyshifted symbols of a short training sequence (STS) 130 as the cyclicallyshifted first training sequence of the cyclically shifted legacy portion112-1 of the preamble, a double guard interval (GI2) 132, cyclicallyshifted symbols of a long training sequence (LTS) 134, 136—repeatedtwice—as the cyclically shifted second training sequence of thecyclically shifted legacy portion 112-1 of the preamble, a guardinterval (GI) 138, and a signal field 139.

As is further shown, the cyclically shifted STS symbols 130 include thesame symbols as the STS symbols 120, but shifted in time by a fraction150 of the duration of the preamble. As mentioned, the fraction 150 mayrange from +/−50 nanoseconds to +/−400 nanoseconds. Similarly, thecyclically shifted LTS symbols 134, 136 include the same symbols as theLTS symbols 134, 136, but shifted in time by the same fraction 150 ofthe duration of the preamble.

In this example, the short training sequence (STS) symbols 120 aretransmitted for a duration of 8 microseconds, as are the cyclicallyshifted STS symbols 130. The signal field 129, 139, which is 4microseconds in duration, includes several bits to indicate the durationof the frame 110. As such, the IEEE 802.11a compliant devices within theproximal area and the 802.11g compliant devices within the proximal areawill recognize frame 110 as being transmitted even though such deviceswill not be able to interpret the remaining portion of the frame. Inthis instance, the legacy devices (IEEE 802.11a and IEEE 802.11g) willavoid a collision with the IEEE 802.11n communication based on a properinterpretation of the legacy portion 112 of the preamble.

The preceding discussion has presented various embodiments for wirelesscommunications in a wireless communication system that includes aplurality of wireless communication devices of differing protocols. Forinstance, more that two transmission antennas may be included in theframe. As one of average skill in the art will appreciate, otherembodiments may be derived from the teachings of the present inventionwithout deviating from the scope of the claims.

Mode Selection Tables:

TABLE 1 2.4 GHz, 20/22 MHz channel BW, 54 Mbps max bit rate Code RateModulation Rate NBPSC NCBPS NDBPS EVM Sensitivity ACR AACR 1 Barker BPSK2 Barker QPSK 5.5 CCK 6 BPSK 0.5 1 48 24 −5 −82 16 32 9 BPSK 0.75 1 4836 −8 −81 15 31 11 CCK 12 QPSK 0.5 2 96 48 −10 −79 13 29 18 QPSK 0.75 296 72 −13 −77 11 27 24 16-QAM 0.5 4 192 96 −16 −74 8 24 36 16-QAM 0.75 4192 144 −19 −70 4 20 48 64-QAM 0.666 6 288 192 −22 −66 0 16 54 64-QAM0.75 6 288 216 −25 −65 −1 15

TABLE 2 Channelization for Table 1 Frequency Channel (MHz) 1 2412 2 24173 2422 4 2427 5 2432 6 2437 7 2442 8 2447 9 2452 10 2457 11 2462 12 2467

TABLE 3 Power Spectral Density (PSD) Mask for Table 1 PSD Mask 1Frequency Offset dBr −9 MHz to 9 MHz 0 +/−11 MHz −20 +/−20 MHz −28 +/−30MHz and −50 greater

TABLE 4 5 GHz, 20 MHz channel BW, 54 Mbps max bit rate Code RateModulation Rate NBPSC NCBPS NDBPS EVM Sensitivity ACR AACR 6 BPSK 0.5 148 24 −5 −82 16 32 9 BPSK 0.75 1 48 36 −8 −81 15 31 12 QPSK 0.5 2 96 48−10 −79 13 29 18 QPSK 0.75 2 96 72 −13 −77 11 27 24 16-QAM 0.5 4 192 96−16 −74 8 24 36 16-QAM 0.75 4 192 144 −19 −70 4 20 48 64-QAM 0.666 6 288192 −22 −66 0 16 54 64-QAM 0.75 6 288 216 −25 −65 −1 15

TABLE 5 Channelization for Table 4 Frequency Frequency Channel (MHz)Country Channel (MHz) Country 240 4920 Japan 244 4940 Japan 248 4960Japan 252 4980 Japan 8 5040 Japan 12 5060 Japan 16 5080 Japan 36 5180USA/Europe 34 5170 Japan 40 5200 USA/Europe 38 5190 Japan 44 5220USA/Europe 42 5210 Japan 48 5240 USA/Europe 46 5230 Japan 52 5260USA/Europe 56 5280 USA/Europe 60 5300 USA/Europe 64 5320 USA/Europe 1005500 USA/Europe 104 5520 USA/Europe 108 5540 USA/Europe 112 5560USA/Europe 116 5580 USA/Europe 120 5600 USA/Europe 124 5620 USA/Europe128 5640 USA/Europe 132 5660 USA/Europe 136 5680 USA/Europe 140 5700USA/Europe 149 5745 USA 153 5765 USA 157 5785 USA 161 5805 USA 165 5825USA

TABLE 6 2.4 GHz, 20 MHz channel BW, 192 Mbps max bit rate ST TX An- CodeModu- Code Rate tennas Rate lation Rate NBPSC NCBPS NDBPS 12 2 1 BPSK0.5 1 48 24 24 2 1 QPSK 0.5 2 96 48 48 2 1 16-QAM 0.5 4 192 96 96 2 164-QAM 0.666 6 288 192 108 2 1 64-QAM 0.75 6 288 216 18 3 1 BPSK 0.5 148 24 36 3 1 QPSK 0.5 2 96 48 72 3 1 16-QAM 0.5 4 192 96 144 3 1 64-QAM0.666 6 288 192 162 3 1 64-QAM 0.75 6 288 216 24 4 1 BPSK 0.5 1 48 24 484 1 QPSK 0.5 2 96 48 96 4 1 16-QAM 0.5 4 192 96 192 4 1 64-QAM 0.666 6288 192 216 4 1 64-QAM 0.75 6 288 216

TABLE 7 Channelization for Table 6 Frequency Channel (MHz) 1 2412 2 24173 2422 4 2427 5 2432 6 2437 7 2442 8 2447 9 2452 10 2457 11 2462 12 2467

TABLE 8 5 GHz, 20 MHz channel BW, 192 Mbps max bit rate ST TX An- CodeModu- Code Rate tennas Rate lation Rate NBPSC NCBPS NDBPS 12 2 1 BPSK0.5 1 48 24 24 2 1 QPSK 0.5 2 96 48 48 2 1 16-QAM 0.5 4 192 96 96 2 164-QAM 0.666 6 288 192 108 2 1 64-QAM 0.75 6 288 216 18 3 1 BPSK 0.5 148 24 36 3 1 QPSK 0.5 2 96 48 72 3 1 16-QAM 0.5 4 192 96 144 3 1 64-QAM0.666 6 288 192 162 3 1 64-QAM 0.75 6 288 216 24 4 1 BPSK 0.5 1 48 24 484 1 QPSK 0.5 2 96 48 96 4 1 16-QAM 0.5 4 192 96 192 4 1 64-QAM 0.666 6288 192 216 4 1 64-QAM 0.75 6 288 216

TABLE 9 channelization for Table 8 Frequency Frequency Channel (MHz)Country Channel (MHz) Country 240 4920 Japan 244 4940 Japan 248 4960Japan 252 4980 Japan 8 5040 Japan 12 5060 Japan 16 5080 Japan 36 5180USA/Europe 34 5170 Japan 40 5200 USA/Europe 38 5190 Japan 44 5220USA/Europe 42 5210 Japan 48 5240 USA/Europe 46 5230 Japan 52 5260USA/Europe 56 5280 USA/Europe 60 5300 USA/Europe 64 5320 USA/Europe 1005500 USA/Europe 104 5520 USA/Europe 108 5540 USA/Europe 112 5560USA/Europe 116 5580 USA/Europe 120 5600 USA/Europe 124 5620 USA/Europe128 5640 USA/Europe 132 5660 USA/Europe 136 5680 USA/Europe 140 5700USA/Europe 149 5745 USA 153 5765 USA 157 5785 USA 161 5805 USA 165 5825USA

TABLE 10 5 GHz, with 40 MHz channels and max bit rate of 486 Mbps TX STCode Code Rate Antennas Rate Modulation Rate NBPSC 13.5 Mbps 1 1 BPSK0.5 1 27 Mbps 1 1 QPSK 0.5 2 54 Mbps 1 1 16-QAM 0.5 4 108 Mbps 1 164-QAM 0.666 6 121.5 Mbps 1 1 64-QAM 0.75 6 27 Mbps 2 1 BPSK 0.5 1 54Mbps 2 1 QPSK 0.5 2 108 Mbps 2 1 16-QAM 0.5 4 216 Mbps 2 1 64-QAM 0.6666 243 Mbps 2 1 64-QAM 0.75 6 40.5 Mbps 3 1 BPSK 0.5 1 81 Mbps 3 1 QPSK0.5 2 162 Mbps 3 1 16-QAM 0.5 4 324 Mbps 3 1 64-QAM 0.666 6 365.5 Mbps 31 64-QAM 0.75 6 54 Mbps 4 1 BPSK 0.5 1 108 Mbps 4 1 QPSK 0.5 2 216 Mbps4 1 16-QAM 0.5 4 432 Mbps 4 1 64-QAM 0.666 6 486 Mbps 4 1 64-QAM 0.75 6

TABLE 11 Power Spectral Density (PSD) mask for Table 10 PSD Mask 2Frequency Offset dBr −19 MHz to 19 MHz 0 +/−21 MHz −20 +/−30 MHz −28+/−40 MHz and −50 greater

TABLE 12 Channelization for Table 10 Frequency Frequency Channel (MHz)Country Channel (MHz) County 242 4930 Japan 250 4970 Japan 12 5060 Japan38 5190 USA/Europe 36 5180 Japan 46 5230 USA/Europe 44 5520 Japan 545270 USA/Europe 62 5310 USA/Europe 102 5510 USA/Europe 110 5550USA/Europe 118 5590 USA/Europe 126 5630 USA/Europe 134 5670 USA/Europe151 5755 USA 159 5795 USA

1. A method for generating a preamble of a frame for a multiple inputmultiple output (MIMO) wireless communication, the method comprises: fora first transmit antenna of the MIMO communication: generating a legacypreamble portion for the frame in accordance with a legacy standardwireless communication protocol, wherein the legacy preamble portionincludes at least a first training sequence and a second trainingsequence and a signal field, wherein the signal field is generated inaccordance with the legacy wireless communication protocol and includesinformation to determine a duration that legacy devices compliant withthe legacy standard wireless communication protocol will not transmit;and generating a current protocol preamble portion for the frame inaccordance with a second current standard wireless communicationprotocol of the MIMO wireless communication; and for at least a secondantenna of the MIMO communication: generating a cyclically shiftedlegacy preamble portion for the frame, wherein the cyclically shiftedlegacy preamble portion includes a cyclically shifted first trainingsequence, a cyclically shifted second training sequence and a cyclicallyshifted signal field, wherein the cyclically shifted legacy preambleportion is time-shifted with respect to the legacy preamble portion; andgenerating a second current protocol preamble portion for the frame inaccordance with the second current standard wireless communicationprotocol of the MIMO wireless communication.
 2. The method of claim 1,wherein the cyclically shifted signal field includes the information todetermine the duration that a legacy device compliant with the legacystandard wireless communication protocol will not transmit.
 3. Themethod of claim 1, wherein when the information is interpreted by thelegacy device compliant with the legacy standard wireless communicationprotocol to determine a duration to not transmit to avoid a collisionwith the MIMO communication.
 4. The method of claim 1, wherein theinformation includes an indication of a duration of the frame.
 5. Themethod of claim 1 wherein the cyclically shifted legacy preamble portionis time-shifted with respect to the legacy preamble portion by afraction of a duration of the legacy preamble portion.
 6. The method ofclaim 1, wherein the legacy wireless communication protocol is at leastone of the following legacy wireless communication standards: IEEE802.11(a), IEEE 802.11(b) and IEEE 802.11(g), and the cyclically shiftedlegacy preamble portion is time-shifted with respect to the legacypreamble portion by at least one of: a range of plus fifty nanosecondsto plus four hundred nanosecond; and a range of minus fifty nanosecondsto minus four hundred nanoseconds.
 7. The method of claim 1, wherein thecurrent protocol preamble portion for the frame is formatted inaccordance with the IEEE 802.11(n) current wireless standardcommunication standard.
 8. The method of claim 1, wherein the firsttraining sequence includes a short training sequence; and the secondtraining sequence includes a long training sequence.
 9. The method ofclaim 1, further comprises: generating a double guard interval betweenthe first and second training sequences in accordance with the legacywireless communication protocol; and generating a second double guardinterval between the first and second cyclically shifted trainingsequences in accordance with the legacy wireless communication protocol.10. A radio frequency (RF) transmitter comprises: a baseband processingmodule that is operably coupled to: for a first transmit antenna of theMIMO communication: generate a legacy preamble portion for the frame inaccordance with a legacy standard wireless communication protocol,wherein the legacy preamble portion includes at least a first trainingsequence and a second training sequence and a signal field, wherein thesignal field is generated in accordance with the legacy wirelesscommunication protocol and includes information for a legacy devicecompliant with the legacy standard wireless communication protocol toavoid a collision with the MIMO communication; and generate a currentprotocol preamble portion for the frame in accordance with a secondcurrent standard wireless communication protocol of the MIMO wirelesscommunication; and for at least a second antenna of the MIMOcommunication: generate a cyclically shifted legacy preamble portion forthe frame, wherein the cyclically shifted legacy preamble portionincludes a cyclically shifted first training sequence, a cyclicallyshifted second training sequence and a cyclically shifted signal field,wherein the cyclically shifted legacy preamble portion is time-shiftedwith respect to the legacy preamble portion; and generate a secondcurrent protocol preamble portion for the frame in accordance with thesecond current standard wireless communication protocol of the MIMOwireless communication.
 11. The RF transmitter of claim 10, wherein thecyclically shifted signal field includes information for a legacy devicecompliant with the legacy standard wireless communication protocol toavoid a collision with the MIMO communication.
 12. The RF transmitter ofclaim 11, wherein when the information is interpreted by the legacydevice compliant with the legacy standard wireless communicationprotocol to determine a duration to not transmit to avoid a collisionwith the MIMO communication.
 13. The RF transmitter of claim 10, whereinthe information includes an indication of a duration of the frame. 14.The RF transmitter of claim 10 wherein the cyclically shifted legacypreamble portion is time-shifted with respect to the legacy preambleportion by a fraction of a duration of the legacy preamble portion. 15.The RF transmitter of claim 10, wherein the legacy wirelesscommunication protocol is at least one of the following legacy wirelesscommunication standards: IEEE 802.11(a), IEEE 802.11(b) and IEEE802.11(g), and the cyclically shifted legacy preamble portion istime-shifted with respect to the legacy preamble portion by at least oneof: a range of plus fifty nanoseconds to plus four hundred nanosecond;and a range of minus fifty nanoseconds to minus four hundrednanoseconds.
 16. The RF transmitter of claim 10, wherein the currentprotocol preamble portion for the frame is formatted in accordance withthe IEEE 802.11(n) current wireless standard communication standard. 17.The RF transmitter of claim 10, wherein the first training sequenceincludes a short training sequence; and the second training sequenceincludes a long training sequence.
 18. The RF transmitter of claim 10,wherein the baseband processing module is further operable to: generatea double guard interval between the first and second training sequencesin accordance with the legacy wireless communication protocol; andgenerate a second double guard interval between the first and secondcyclically shifted training sequences in accordance with the legacywireless communication protocol.